I have advanced further in the game and I have to say that I disagree with this point now. There are two sets of very strong heavy armors that not only provide high protection, but also receive a BONUS when you wear all the pieces of the armor together. The first set bonus provides a ton of damage, the other provides a ton of health. So, while I still agree that for the majority of the game you should focus on LIGHT armors for the Barbarian and invest somewhere else, you better upgrade your Armor skills to 4+ for your last levels. These bonus are so good that I made my dual wield DEX rogue to wear one the armors + the shield of the set.Barbarian
Heavy Armor vs Light Armor: Heavy armors tend to give high protection, and extra health. Light armors tend to give decent protection, and extra evasion. That being said, the best armor pieces for barbarians are +STR light armors. If I knew this back at the character creation, I wouldn't specialize my barbarian in heavy armor. By not investing so much in armor, I can get an extra 2 to 3 free points to invest somewhere else.
Here are the builds of my characters:
STR Barbarian => 5 HW, 2+ Critical, 4+ Armor, 4+ Accuracy (Armor set that provides health)
DEX Rogue => 5 LW, 5 Critical, 4+ Armor, 2+ Accuracy (Armor set that provides damage)
Ranged DEX ROGUE => (Clothes set that provides DEX)
Wizard => (Clothes set that provides WIL)